The present disclosure relates generally to downhole systems and methods for active cooling of equipment that is deployed in boreholes traversing subterranean formations. More particularly, the present disclosure relates to techniques for circulating cooling fluids in a borehole to provide significant reduction in downhole temperatures.
Logging and monitoring boreholes has been done for many years to enhance and observe recovery of oil and gas deposits. In the logging of boreholes, one method of making measurements underground includes attaching one or more tools to a wireline connected to a surface system. The tools are then lowered into a borehole by the wireline and drawn back to the surface (“logged”) through the borehole while taking measurements. Similarly, permanent monitoring systems are established with permanent sensors that are also generally attached to an electrical cable.
The complexity of petro-physical and seismic logging jobs is increasing with time as demands for longer exposures and higher temperatures are placed on the downhole equipment. Even in the case of more robust and reliable technology for downhole circuitry such as analog and/or electronic, there is a need for lowering the temperatures in boreholes so that any type of circuitry can survive downhole for longer periods of time during semi-permanent deployments or in long logging surveys. In high temperature conditions and long exposure logging conditions, both the cost of maintenance and part replacement become very high and labor intensive regardless of the technology that is employed in the downhole circuitry.
In addition, while the cooling of equipment downhole is desirable, many tools in current use would have to be completely reworked or replaced to incorporate new cooling technologies. Furthermore, typically downhole tools are rated or designed for specific operating temperature ranges. It would be desirable to facilitate active cooling with minimal changes to existing tools and equipment. It would also be desirable to use existing tools and equipment at operating temperatures that exceed the design specifications without damaging or extensively modifying the tools or equipment.
The limitations of conventional designs noted in the preceding are not intended to be exhaustive but rather are among many which may reduce the effectiveness of previously known downhole mechanisms.